In the non-invasive inspection field, X-ray is an important transmission inspection means. For example, after performing X-ray radiation imaging on a vehicle, a prohibited item in the vehicle can be inspected by reviewing and analyzing X-ray scan images, to thereby reach the objective of security inspection.
At present, the X-ray use in transmission inspection has been upgraded from a single energy ray to a high and low dual-energy ray, and the recognition of an object to be inspected is advanced by leaps and bounds based on a difference in penetration characteristics of dual-energy ray.
The main technical indexes for the current security inspection apparatus comprise transmissivity and spatial wire resolution of X-ray. The so-called spatial wire resolution is a degree to which a detector can recognize an iron wire (the diameter of the iron wire is for example 1 mm or 2 mm or etc.) in a space, when the X-ray is irradiated into the iron wire. High energy photons are favorable to the index of transmissivity, because the high energy photons can improve the penetration capability of the ray, but the high energy photons are very unfavorable to the spatial wire resolution, because the high energy photons lost a great amount of information of the object to be inspected. Low energy ray has a better spatial wire resolution, and the low energy ray can image by irradiating the spatial wires.
The energy spectrum of the X-ray is a continuous spectrum, and a low energy portion of its high energy ray influences the transmissivity of the high energy ray. By adding a filter for absorbing low energy photons in a beam exit direction of the ray source, the transmissivity of the high energy ray can be improved, but the spatial wire resolution of the low energy ray will be reduced at the same time. Thus, a problem to be solved in the dual-energy X-ray inspection technology is how to guarantee the index of transmissivity and the index of spatial wire resolution at the same time.